# US 12,222,411 B2 · Magnetic resonance imaging system and method using frequency calibration based on a signal from a geo-satellite positioning system

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- Number: US 12,222,411 B2
- Document ID: US12222411B2
- Status: Granted
- Kind: B2
- Application number: 18/014,563
- Filed: 2021-06-22
- Published: 2023-08-17
- Granted: 2025-02-11
- Earliest claimed: 2020-07-07
- Assignees: Koninklijke Philips N.V.
- Applicants: Koninklijke Philips N.V.
- Inventors: Tim Nielsen; Christoph Günther Leussler; Peter Vernickel; Oliver Lips
- Web page: https://patentgrep.com/patent/US12222411B2

## CPC

- G01R 33/3692: {involving signal transmission without using electrically conductive connections, e.g. wireless communication or optical communication of the MR signal or an auxiliary signal other than the MR signal}
- G01R 33/24: for measuring direction or magnitude of magnetic fields or magnetic flux
- G01R 33/3607: {RF waveform generators, e.g. frequency generators, amplitude-, frequency- or phase modulators or shifters, pulse programmers, digital to analog converters for the RF signal, means for filtering or attenuating of the RF signal}
- G01R 33/3621: {NMR receivers or demodulators, e.g. preamplifiers, means for frequency modulation of the MR signal using a digital down converter, means for analog to digital conversion [ADC] or for filtering or processing of the MR signal such as bandpass filtering, resampling, decimation or interpolation}
- G01R 33/56563: {caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 (G01R33/56509, G01R33/56518, G01R33/56536 take precedence)}
- G01R 33/583: {Calibration of signal excitation or detection systems, e.g. for optimal RF excitation power or frequency (G01R33/246 takes precedence)}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A method of setting an RF operating frequency of an MRI system (1) uses a first reference frequency signal, obtained from a geo-satellite positioning system, as a stable long term frequency reference. A second frequency source (24) is calibrated using the first frequency reference signal and the second frequency reference source (24) is then used as the master clock for the MRI system (1), for setting the RF operating frequency.

## Claims

### Claim 1

A method of setting an RF operating frequency of an MRI system for RF synthesis and reception, comprising:
using a first reference frequency signal, obtained from a geo-satellite positioning system, as a stable frequency reference;
obtaining calibration information for a second frequency source for determining the true frequency, using the first reference frequency signal;
setting the RF operating frequency, using the second frequency source as the master clock for the MRI system, and using the calibration information; and
measuring the RF operating frequency by:
placing a magnetic resonance signal probe into the imaging bore of the MRI system; and
measuring a free induction decay using the magnetic resonance signal probe, wherein the magnetic resonance signal probe comprises a frequency reference which is calibrated by a signal obtained from a geo-satellite positioning system.

### Claim 2

A system for setting an RF operating frequency of an MRI system for RF synthesis and reception, comprising:
an antenna for receiving a first reference frequency signal (CLK1), from a geo-satellite positioning system, as a stable frequency reference;
a second frequency source for functioning as the master clock for the MRI system for setting the RF operating frequency (F0);
a calibration system for obtaining calibration information for the second frequency source using the first reference frequency signal; and
a magnetic resonance signal probe for insertion into the imaging bore of the MRI system for measuring a free induction decay, wherein the magnetic resonance signal probe comprises a frequency reference which is calibrated by a signal obtained from a geo-satellite positioning system.

### Claim 3 (depends on 1)

The method of claim 1, wherein the first reference frequency signal is obtained from a GPS system.

### Claim 4 (depends on 1)

The method of claim 1, wherein the second frequency source comprises an oven controlled crystal oscillator.

### Claim 5 (depends on 1)

The method of claim 1, comprising measuring the free induction decay with a subject in the imaging bore of the MRI system and without a subject in an imaging bore of the MRI system.

### Claim 6 (depends on 1)

The method of claim 1, further comprising performing a resonant frequency calibration using the MRI system, and determining the master clock frequency based on the resonant frequency calibration and the measurement of the free induction decay using the magnetic resonance signal probe.

### Claim 7 (depends on 2)

The system of claim 2, wherein the antenna comprises a GPS antenna.

### Claim 8 (depends on 2)

The system of claim 2, wherein the second frequency source comprises an oven controlled crystal oscillator.

### Claim 9 (depends on 2)

The system of claim 2, wherein the probe comprises an MR-active substance and an RF coil to excite the magnetization and detect the magnetic resonance signal.

### Claim 10 (depends on 2)

The system of claim 2, comprising an array of magnetic resonance signal probes for insertion into the imaging bore of the MRI system.

### Claim 11 (depends on 2)

The system of claim 2, wherein the magnetic resonance signal probe comprises a geo-satellite receiver.

### Claim 12 (depends on 1)

The method of claim 1, wherein the magnetic resonance signal probe comprises a geo-satellite receiver.

### Claim 13 (depends on 1)

The method of claim 1, wherein the geo-satellite receiver comprises a global positioning system (GPS) receiver.

### Claim 14 (depends on 5)

The method of claim 5, comprising placing an array of magnetic resonance signal probes into the imaging bore of the MRI system and measuring a free induction decay using each magnetic resonance signal probe.

### Claim 15 (depends on 5)

The method of claim 5, comprising monitoring the temporal characteristics of the field detected by the probe to detect subject-induced variations.

### Claim 16 (depends on 6)

The method of claim 6, comprising modeling an expected resonance frequency using a trained model to determine the required resonance frequency for imaging.

### Claim 17 (depends on 10)

The system of claim 10, wherein the free induction decay is measured with a subject in the imaging bore of the MRI system and without a subject in an imaging bore of the MRI system.

### Claim 18 (depends on 10)

The system of claim 10, wherein the temporal characteristics of the field detected by the probe are monitored to detect subject-induced variations.

### Claim 19 (depends on 11)

The system of claim 11, wherein the geo-satellite receiver comprises a global positioning system (GPS) receiver.

### Claim 20 (depends on 16)

The method of claim 16, wherein the training data for the model comprises the resonance frequency, main field maps of patients, and additional patient data available during examination.